Several methods are known to lay pipelines from a pipe-lay vessel on a seabed. The present invention relates to J-lay. With the J-lay method, a pipeline is supported by its free end from the pipe-lay vessel and new pipe sections are joined to the free end. The formed pipeline is lowered into the water in a near vertical position via a J-lay tower. The J-lay tower is equipped with one or more working stations where the pipe sections are welded to the end of the already completed pipeline. Other activities may involve application of field joint coating, or installation of appurtenances like anodes and VIV strakes.
The welding process is sensitive for draught and moisture. In order to prevent draught and moisture from reaching a welding zone, the workstation comprises a roof. Since the lengths of pipe that are welded together are in general longer than the height of the working station, the pipe section will penetrate through the roof of the station.
Normally, the roof of the welding station is closed when welding takes place, in order to prevent draught or rain from disrupting the welding process. When the pipe is lowered or during other activities, the roof is opened again, for instance to allow passage of a travelling block.
It is well known to apply a seal between the roof and the pipe to prevent draught and water ingress, in particular when it is raining during welding operations. Known seals are based on contact between the sealing device and the pipeline to close off any gaps. Normally, a flexible material is used at the contact area of the seal, for instance rubber. However, other materials may also be used.
It is found in practice that it is difficult to make a contact seal that completely prevents water to run down the pipe towards the welding area. Because the roof of the welding station is made up from several parts that are moved during opening or closing, the sealing device also needs to be made out of multiple sections to allow passage of items larger than the pipeline. To create a watertight seal, the seams of the different parts of the seal need to be perfectly aligned. This is difficult to realize.